American women are taking around 2 ½ hours more to give birth these days than women did five decades ago, according to a fresh report.

A team of researchers led by Dr. Katherine Laughon, an epidemiologist with the Eunice Kennedy Shriver National Institute of Child Health & Human Development, gathered data on as many as 40,000 women who delivered between 1959 and 1966, and compared the data around 100,000 women who gave birth between 2002 and 2008.

Researchers found that the typical first-time mother in America is now taking 6 1/2 hours to deliver, while her counterpart five decades ago labored for hardly 4 hours.

Researchers held older maternal age and increase in body-mass index (BMI), a ratio of weight to height, responsible for a part of longer labors.

Explaining the reasons for longer labors, Dr. Laughon said, "Older maternal age and increased BMI accounted for a part of the increase. We believe that some aspects of delivery-room practice are also responsible for this increase."

The longer labors will prompt surgeons to reassess when they should draw the line for cesarean delivery, which costs around $17,000 as compared with $9,400 for giving birth through vagina.

Last year, researchers at Intermountain Healthcare estimated that the country could save up to $3.5 billion by lowering the rate of national cesarean delivery from 32 per cent to 21 per cent.